1. Field of the Invention
The invention relates to a method and apparatus for evaluating the efficiency of rolling contact bearings which are used, for example, in disk drive data storage devices.
2. Description of the Related Art
Rolling contact bearings are utilized in numerous mechanical applications to transfer loads between rotating and stationary structures, (or two rotating structures), to permit free movement of rotating elements with minimal friction. Such bearings have a typical structure which is characterized by an inner ring or "race", an outer race, and rotating elements, such as balls or rollers, separating the inner and outer races. In addition, cages are typically used to separate the rotating elements from each other.
Rolling contact bearings are a key component of Winchester-type hard disk drive storage devices. An exemplary use of rolling contract bearings in such a drive is shown in FIGS. 11A-11B. FIGS. 11A and 11B are partial, cross-sectional views of a typical Winchester-type hard disk drive, wherein data is stored on a disk 22 by read/write heads 60A, 60B, positioned with respect to a disk by a rotary-type actuator assembly. The rotary-type actuator includes: actuator arm 52 having first and second subarms 52A, 52B, for supporting load beams 54A, 54B, respectively, on which read/write heads 60A, 60B, are mounted; a bearing assembly 40; and a voice coil motor assembly, including coil 70 and magnet 66.
The disk drive shown incorporates two bearing assemblies each having two rotary bearings translating loads between the stationary disk housing and rotary elements. A first bearing assembly is utilized to allow actuator body 52 to rotate about stationary mounting post 42, secured in base 12 on the disk drives. This first bearing assembly comprises two bearings 46 mounted in a bearing cartridge 40. A second bearing structure, comprising bearings 36 and 37, is used for supporting a spindle motor and hub assembly to allow for rotation of disk 22, shaft 35, and hub 41 with respect to base 12.
As shown in FIG. 11B, actuator bearing cartridge 40 is comprised of two single row radial bearings 46, each having an inner race 47A and outer race 47B, separated by balls 49. Bearing cartridge 40, includes an outer casing 48 in which bearings 46 are preloaded and separated by a spacer 44. Preloading of bearings 46 in this manner facilitates final assembly of the actuator in the disk drive. Bearings 36 and 37 may also comprise single row radial bearings (not detailed) which separate mounting shelf 34 for the disk 22 from the base 12. In normal drive operation, actuator 52 positions head 60A, 60B about a rotational axis 30 passing through the center of hex screw 45, used to secure mounting post 42 to base 12. Actuator 52 positions read/write heads 60A,60B at individual tracks on each surface of disk 22 under the direction of control electronics to read and write data therefrom. The force required to move actuator 52 is provided by a voice coil motor comprising magnet 66 and coil 70. Magnet 66 is arranged so that a current in coil 70, in relation to the magnetic field generated by magnet 66, controls positioning of actuator 52 around rotational axis 30. Typically the density of individual tracks on disk 22 is on the order of 2,000 tracks per inch. Thus, the accuracy required for positioning actuator 52 is extremely high. In addition, such disk drives are designed and manufactured to meet certain predetermined performance specifications, including, for example, data access times and actuator seek times which are, in part, related to the efficiency with which actuator 52 may be positioned. Thus, the running friction between the inner and outer rates of bearings 46 comprising cartridge 40 affects the overall drive performance specifications for the drive. Hence, it is important that the bearing cartridge 40 operate within the required design specifications to ensure the actuator's movement relative to support post 42.
Furthermore, seek times are related to spindle motor efficiency and the speed at which disk 22 is rotated about shaft 35. Thus, operation of bearings 36 and 37 is also crucial to the drive's ability to perform to specifications.
Generally, the rolling contact bearings utilized in disk drives are supplied to the disk drive manufacturer by an outside vendor and are represented as having the ability to operate within the drive manufacturer's defined specifications. There is therefore little opportunity for the drive manufacturer to implement quality control over bearing manufacture. A percentage of all the bearings supplied to the disk drive manufacturer do not meet the defined specifications and have a unacceptably high degree of running friction. Running friction is defined as the friction between the inner and outer races of the bearing, measurable as a resistance torque.
As a means for ensuring quality in the manufactured disk drive, systems for testing the running friction in such bearings are available. One such system manufactured by Vibrac Corporation, is available for testing the running friction between the inner and out races of one rolling contact bearing, such as those shown in FIGS. 11A and 11B. However, such conventional systems are generally extremely large and cumbersome, and require a large amount of floor space dedicated for the use of the device. Such devices are not suitable for easy movement to a number of locations. Further, conventional devices are currently limited to one bearing test station per device, thus allowing only one separate bearing to be tested at any one particular time by the testing unit.
Thus, an object of the invention is to provide an improved method and apparatus for testing rolling contact bearings.
A further object of the invention is to provide a method and apparatus for testing rolling contact bearings which has a reduced size and ease of portability.
Another object of the invention is to provide a system for testing rolling contact bearings which may include up to eight separate bearing testing stations coupled to a single control means.
A further object of the invention is to provide a apparatus and method for testing rolling contact bearings which are utilized in disk drives, and specifically, a system which may be adapted to test various different sizes of rolling contact bearings.
Yet another object of the invention is to provide a system for testing rolling contact bearings which is adaptable for testing assembled bearing cartridges utilized in disk drive storage devices.